Message-ID: <20251006100130.2623388-2-alejandro.lucero-palau@amd.com>
Date: Mon, 6 Oct 2025 11:01:09 +0100
From: <alejandro.lucero-palau@....com>
To: <linux-cxl@...r.kernel.org>, <netdev@...r.kernel.org>,
	<dan.j.williams@...el.com>, <edward.cree@....com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <edumazet@...gle.com>,
	<dave.jiang@...el.com>
CC: Alejandro Lucero <alucerop@....com>
Subject: [PATCH v19 01/22] cxl/mem: Arrange for always-synchronous memdev attach

From: Alejandro Lucero <alucerop@....com>

In preparation for CXL accelerator drivers that have a hard dependency on
CXL capability initialization, arrange for the endpoint probe result to be
conveyed to the caller of devm_cxl_add_memdev().

As it stands cxl_pci does not care about the attach state of the cxl_memdev
because all generic memory expansion functionality can be handled by the
cxl_core. For accelerators, that driver needs to know perform driver
specific initialization if CXL is available, or exectute a fallback to PCIe
only operation.

By moving devm_cxl_add_memdev() to cxl_mem.ko it removes async module
loading as one reason that a memdev may not be attached upon return from
devm_cxl_add_memdev().

The diff is busy as this moves cxl_memdev_alloc() down below the definition
of cxl_memdev_fops and introduces devm_cxl_memdev_add_or_reset() to
preclude needing to export more symbols from the cxl_core.

Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/cxl/Kconfig       |  2 +-
 drivers/cxl/core/memdev.c | 97 ++++++++++++++++-----------------------
 drivers/cxl/mem.c         | 30 ++++++++++++
 drivers/cxl/private.h     | 11 +++++
 4 files changed, 82 insertions(+), 58 deletions(-)
 create mode 100644 drivers/cxl/private.h

diff --git a/drivers/cxl/Kconfig b/drivers/cxl/Kconfig
index 028201e24523..111e05615f09 100644
--- a/drivers/cxl/Kconfig
+++ b/drivers/cxl/Kconfig
@@ -22,6 +22,7 @@ if CXL_BUS
 config CXL_PCI
 	tristate "PCI manageability"
 	default CXL_BUS
+	select CXL_MEM
 	help
 	  The CXL specification defines a "CXL memory device" sub-class in the
 	  PCI "memory controller" base class of devices. Device's identified by
@@ -89,7 +90,6 @@ config CXL_PMEM
 
 config CXL_MEM
 	tristate "CXL: Memory Expansion"
-	depends on CXL_PCI
 	default CXL_BUS
 	help
 	  The CXL.mem protocol allows a device to act as a provider of "System
diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
index c569e00a511f..2bef231008df 100644
--- a/drivers/cxl/core/memdev.c
+++ b/drivers/cxl/core/memdev.c
@@ -8,6 +8,7 @@
 #include <linux/idr.h>
 #include <linux/pci.h>
 #include <cxlmem.h>
+#include "private.h"
 #include "trace.h"
 #include "core.h"
 
@@ -620,42 +621,30 @@ static void detach_memdev(struct work_struct *work)
 
 static struct lock_class_key cxl_memdev_key;
 
-static struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds,
-					   const struct file_operations *fops)
+struct cxl_memdev *devm_cxl_memdev_add_or_reset(struct device *host,
+						struct cxl_memdev *cxlmd)
 {
-	struct cxl_memdev *cxlmd;
-	struct device *dev;
-	struct cdev *cdev;
+	struct device *dev = &cxlmd->dev;
+	struct cdev *cdev = &cxlmd->cdev;
 	int rc;
 
-	cxlmd = kzalloc(sizeof(*cxlmd), GFP_KERNEL);
-	if (!cxlmd)
-		return ERR_PTR(-ENOMEM);
-
-	rc = ida_alloc_max(&cxl_memdev_ida, CXL_MEM_MAX_DEVS - 1, GFP_KERNEL);
-	if (rc < 0)
-		goto err;
-	cxlmd->id = rc;
-	cxlmd->depth = -1;
-
-	dev = &cxlmd->dev;
-	device_initialize(dev);
-	lockdep_set_class(&dev->mutex, &cxl_memdev_key);
-	dev->parent = cxlds->dev;
-	dev->bus = &cxl_bus_type;
-	dev->devt = MKDEV(cxl_mem_major, cxlmd->id);
-	dev->type = &cxl_memdev_type;
-	device_set_pm_not_required(dev);
-	INIT_WORK(&cxlmd->detach_work, detach_memdev);
+	rc = cdev_device_add(cdev, dev);
+	if (rc) {
+		/*
+		 * The cdev was briefly live, shutdown any ioctl operations that
+		 * saw that state.
+		 */
+		cxl_memdev_shutdown(dev);
+		put_device(dev);
+		return ERR_PTR(rc);
+	}
 
-	cdev = &cxlmd->cdev;
-	cdev_init(cdev, fops);
+	rc = devm_add_action_or_reset(host, cxl_memdev_unregister, cxlmd);
+	if (rc)
+		return ERR_PTR(rc);
 	return cxlmd;
-
-err:
-	kfree(cxlmd);
-	return ERR_PTR(rc);
 }
+EXPORT_SYMBOL_NS_GPL(devm_cxl_memdev_add_or_reset, "CXL");
 
 static long __cxl_memdev_ioctl(struct cxl_memdev *cxlmd, unsigned int cmd,
 			       unsigned long arg)
@@ -1023,50 +1012,44 @@ static const struct file_operations cxl_memdev_fops = {
 	.llseek = noop_llseek,
 };
 
-struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
-				       struct cxl_dev_state *cxlds)
+struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds)
 {
 	struct cxl_memdev *cxlmd;
 	struct device *dev;
 	struct cdev *cdev;
 	int rc;
 
-	cxlmd = cxl_memdev_alloc(cxlds, &cxl_memdev_fops);
-	if (IS_ERR(cxlmd))
-		return cxlmd;
+	cxlmd = kzalloc(sizeof(*cxlmd), GFP_KERNEL);
+	if (!cxlmd)
+		return ERR_PTR(-ENOMEM);
 
-	dev = &cxlmd->dev;
-	rc = dev_set_name(dev, "mem%d", cxlmd->id);
-	if (rc)
+	rc = ida_alloc_max(&cxl_memdev_ida, CXL_MEM_MAX_DEVS - 1, GFP_KERNEL);
+	if (rc < 0)
 		goto err;
-
-	/*
-	 * Activate ioctl operations, no cxl_memdev_rwsem manipulation
-	 * needed as this is ordered with cdev_add() publishing the device.
-	 */
+	cxlmd->id = rc;
+	cxlmd->depth = -1;
 	cxlmd->cxlds = cxlds;
 	cxlds->cxlmd = cxlmd;
 
-	cdev = &cxlmd->cdev;
-	rc = cdev_device_add(cdev, dev);
-	if (rc)
-		goto err;
+	dev = &cxlmd->dev;
+	device_initialize(dev);
+	lockdep_set_class(&dev->mutex, &cxl_memdev_key);
+	dev->parent = cxlds->dev;
+	dev->bus = &cxl_bus_type;
+	dev->devt = MKDEV(cxl_mem_major, cxlmd->id);
+	dev->type = &cxl_memdev_type;
+	device_set_pm_not_required(dev);
+	INIT_WORK(&cxlmd->detach_work, detach_memdev);
 
-	rc = devm_add_action_or_reset(host, cxl_memdev_unregister, cxlmd);
-	if (rc)
-		return ERR_PTR(rc);
+	cdev = &cxlmd->cdev;
+	cdev_init(cdev, &cxl_memdev_fops);
 	return cxlmd;
 
 err:
-	/*
-	 * The cdev was briefly live, shutdown any ioctl operations that
-	 * saw that state.
-	 */
-	cxl_memdev_shutdown(dev);
-	put_device(dev);
+	kfree(cxlmd);
 	return ERR_PTR(rc);
 }
-EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
+EXPORT_SYMBOL_NS_GPL(cxl_memdev_alloc, "CXL");
 
 static void sanitize_teardown_notifier(void *data)
 {
diff --git a/drivers/cxl/mem.c b/drivers/cxl/mem.c
index f7dc0ba8905d..144749b9c818 100644
--- a/drivers/cxl/mem.c
+++ b/drivers/cxl/mem.c
@@ -7,6 +7,7 @@
 
 #include "cxlmem.h"
 #include "cxlpci.h"
+#include "private.h"
 #include "core/core.h"
 
 /**
@@ -203,6 +204,34 @@ static int cxl_mem_probe(struct device *dev)
 	return devm_add_action_or_reset(dev, enable_suspend, NULL);
 }
 
+/**
+ * devm_cxl_add_memdev - Add a CXL memory device
+ * @host: devres alloc/release context and parent for the memdev
+ * @cxlds: CXL device state to associate with the memdev
+ *
+ * Upon return the device will have had a chance to attach to the
+ * cxl_mem driver, but may fail if the CXL topology is not ready
+ * (hardware CXL link down, or software platform CXL root not attached)
+ */
+struct cxl_memdev *devm_cxl_add_memdev(struct device *host,
+				       struct cxl_dev_state *cxlds)
+{
+	struct cxl_memdev *cxlmd = cxl_memdev_alloc(cxlds);
+	int rc;
+
+	if (IS_ERR(cxlmd))
+		return cxlmd;
+
+	rc = dev_set_name(&cxlmd->dev, "mem%d", cxlmd->id);
+	if (rc) {
+		put_device(&cxlmd->dev);
+		return ERR_PTR(rc);
+	}
+
+	return devm_cxl_memdev_add_or_reset(host, cxlmd);
+}
+EXPORT_SYMBOL_NS_GPL(devm_cxl_add_memdev, "CXL");
+
 static ssize_t trigger_poison_list_store(struct device *dev,
 					 struct device_attribute *attr,
 					 const char *buf, size_t len)
@@ -250,6 +279,7 @@ static struct cxl_driver cxl_mem_driver = {
 	.probe = cxl_mem_probe,
 	.id = CXL_DEVICE_MEMORY_EXPANDER,
 	.drv = {
+		.probe_type = PROBE_FORCE_SYNCHRONOUS,
 		.dev_groups = cxl_mem_groups,
 	},
 };
diff --git a/drivers/cxl/private.h b/drivers/cxl/private.h
new file mode 100644
index 000000000000..bdeb66e4a04f
--- /dev/null
+++ b/drivers/cxl/private.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* Copyright(c) 2025 Intel Corporation. */
+
+/* Private interfaces betwen common drivers ("cxl_mem") and the cxl_core */
+
+#ifndef __CXL_PRIVATE_H__
+#define __CXL_PRIVATE_H__
+struct cxl_memdev *cxl_memdev_alloc(struct cxl_dev_state *cxlds);
+struct cxl_memdev *devm_cxl_memdev_add_or_reset(struct device *host,
+						struct cxl_memdev *cxlmd);
+#endif /* __CXL_PRIVATE_H__ */
-- 
2.34.1

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